class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        '''
        :param haystack:
        :param needle:
        :return:
        用python实现字符串匹配问题
        (1)如果索要查找的字符串或者子字符串的长度为0，则返回False
        (2)如果总字符串的长度小于所要查找的子字符串的长度，则返回False
        (3)将i从0到len(father)-len(sub)
        如果 father[i:(i+len(sub)]==sub 则返回True，break
        否则 i+=1 进入下一次循环
        跳出循环后，返回False
        '''
        if not len(haystack) and not len(needle):
            return 0
        if not len(haystack):
            return -1
        if not len(needle):
            return 0
        if len(haystack) < len(needle):
            return -1
        for i in range(0, len(haystack) - len(needle) + 1):
            if haystack[i:(i + len(needle))] == needle:
                return i
        return -1